Semiconductor devices are mass produced by forming many identical circuit patterns on a single silicon wafer which is thereafter cut into many identical dies or "chips." Semiconductor devices, also commonly referred to as integrated circuits, are typically constructed by successively depositing or "stacking" layers of various materials on the wafer. Many of these layers are etched according to a predetermined pattern as part of the formation of the desired circuit components. Some of these materials are deposited, patterned and etched using processing techniques that require the introduction of gases into a reaction chamber or vessel. The gases react with one another and with the surface of the semiconductor wafers to deposit or remove the desired materials. For example, chemical vapor deposition ("CVD") and dry or "plasma" etching are two common semiconductor manufacturing processes that use reactant gases to deposit materials on and selectively remove materials from the surface of a semiconductor wafer.
Mass flow controllers are used to monitor and control the flow of the gases into the reaction chamber in CVD, plasma etching and other such semiconductor manufacturing processes. Mass flow controllers are used whenever accurate measurement and control of gas is required. A typical mass flow controller has two primary operational components--a mass flow meter and a proportioning controller. The flow meter measures the actual flow. The controller drives a variable displacement valve to the correct position to maintain the desired flow. The gas flows through three primary and discrete physical components in the mass flow controller--the inlet, the main body and the outlet. In one common configuration, the variable displacement valve is positioned in the inlet and the flow meter is positioned in the main body. Each of the above described components must be sealed one to the other to achieve effective operation of the mass flow controller. Mass flow controllers must be periodically disassembled for cleaning and repairing or replacing worn or malfunctioning parts. Upon re-assembly, care must be taken to ensure that the respective components are properly sealed. The latest generation of mass flow controllers, such as a Unit Instruments, Inc. Model UFC-1600 or Precision Flow Devices Model PFD 501M, utilize metal seals to effect a seal between the component surfaces. Metal seals require that the components be precisely aligned to effect the uniform distribution of tightening forces before the fasteners are tightened to secure and seal the components. In addition, metal seals require the application of much higher torque values to adequately tighten the fasteners.
Experience with the metal seals used in modern mass flow controllers has shown that it is difficult to obtain an effective seal unless the mass flow controller components are clamped together with evenly distributed pressure. The fasteners can then be uniformly tightened to meet the required torque specifications. In the past, the mass flow controller components were clamped together using an ordinary bench mounted vice. Obtaining a satisfactory seal using a vice is difficult and time consuming, particularly because the controller could not be readily and properly positioned for clamping. Unit Instruments, Inc. developed a prototype clamping device for use with its mass flow controllers. Like the bench vise, the Unit prototype did not afford the operator any way to support and accurately position the controller for clamping. The absence of a support/positioning mechanism and its substantial weight made the Unit prototype cumbersome to use and ineffective in consistently obtaining a reliable seal. The Unit prototype also was not adaptable for use with other brands of mass flow controllers.